This invention relates to a manufactured granular substrate suitable for use as a carrier for chemical agents, as well as a method for producing a granular substrate. More particularly, this invention relates to a light weight manufactured granular substrate.
Generally, manufactured granular substrates are utilized as carriers for active chemical agents, such as for example herbicides or other pesticides. The carriers, with the active chemical agents, are utilized to distribute the active agent over a broad area. The carriers are generally inert compounds that, upon application, break down over time. Existing carrier compositions have larger than desired particle sizes accompanied by high bulk densities of greater than 60 pounds per cubic foot. It is preferable to utilize a carrier with smaller granules and a lower bulk density in order to efficiently transport and distribute the required amount of active chemical agent without utilizing excessive amounts of inert carrier compounds.
In addition, conventional manufactured granular substrates often have a tendency to break apart thus creating handling and distribution problems. Granular substrates that resist attrition are preferred because they will not degrade and therefore maintain their particle size during handling. While resistance to attrition is important, it may also be preferable that the carrier compound breakdown or disintegrate upon exposure to water.
U.S. Pat. No. 5,078,779 discloses a binder composition for the granulation of dry, stable, particulate fertilizers. The composition generally includes a reactive carbonate and a reactive sulfate, in combination with a silicate strengthening agent and a water dispersing agent. Dolomite is disclosed as a carbonate source for the binder composition. The binder is used in conjunction with ammonium sulfate to provide a granulated fertilizer. In order to form the granulated fertilizer, the patent teaches the use of a reactive acid to initiate a reaction between the sulfate salt and the metal ion of the carbonate to form a complex salt.
A manufactured granular substrate having 10% to 100% plant fiber and 0% to 90% of a mineral filler is disclosed in U.S. Pat. No. 5,019,564. The substrate is formed by the agitated agglomeration of a fibrous slurry without the use of a binder. The plant fibers are generally 1 mm to 10 mm in length. The resulting substrate has a bulk density of about 20 to 42 pounds per cubic foot. The substrate is utilized as a carrier for active chemical agents. However, the substrate does not readily breakdown upon exposure to water. Additionally, the fibrous nature of the substrate can reduce the ability of the substrate to flow in bulk form.
U.S. Pat. Nos. 4,015,973, 4,954,134, and 5,228,895 all generally disclose the use of either limestone or dolomite in conjunction with a lignosulfonate binder in the formation of manufactured granular substrates. The agglomerated particles produced in accordance with the patents are either outside the preferred size and bulk density or are susceptible to degradation during handling.
Additionally, U.S. Pat. No. 5,242,690 discloses an inert manufactured granular substrate as a carrier for chemical agents. The granular carrier composition includes grain dust and a binder of either calcium or sodium lignosulfonate. The finished granular carrier exhibits a bulk density between 30 and 35 lbs per cubic foot.
Thus, existing manufactured granular substrates utilize either limestone or dolomite with other binding or reactive components to produce granular substrates as carriers for active chemical agents. The existing manufactured granular substrates are not of the desired size or bulk density. Also, some of the existing manufactured granular substrates have a tendency to breakdown during handling thereby changing the bulk density or creating distribution problems during application. Other granular substrates, produced from primarily plant fiber, have some desirable physical properties but fail to readily disintegrate upon exposure to water.
It would be an advantage to produce a manufactured granular substrate for use as a carrier compound for active chemical agents that has a bulk density of less than about 55 pounds per cubic foot at a relatively small particle size. A manufactured granular substrate having the noted properties is capable of delivering an appropriate amount of active chemical agent to a desired area while utilizing less inert material. Furthermore, smaller particle sizes provide a greater surface area for the chemical agent and result in an improved distribution or coverage of the desired area of application.
It would also be an advantage to produce a manufactured granular substrate that does not degrade during handling but preferably breaks down when exposed to moisture or water. The resistance to attrition ensures the proper distribution of the active chemical agent upon application. Furthermore, the ability to disintegrate upon exposure to water is preferred to provide the active chemical agent to the soil.
In accordance with the present invention, there is provided a novel manufactured granular substrate composition that is suitable for use as a carrier for active chemical agents. The present invention also includes a method for forming the manufactured granular substrate.
The manufactured granular substrate composition of the present invention includes one or more mineral components, one or more light weight additives, and one or more binders. The mineral component in the granular substrate is preferably selected from the group consisting of dolomite, limestone and gypsum. The light weight additive is preferably of one or more compounds selected from the group consisting of expanded silica, fly ash, hydrated lime, wheat flour, wood flour, ground wheat straw, cellulose and soy flour. The binder may preferably be one or more materials selected from the group consisting of brewers condensed solubles, lignosulfonate, sodium carbonate lignin, cane molasses, beet syrup, beet molasses, desugared beet molasses, whey, starch, starch derivatives, soy solubles with cane molasses or the like, hydrolyzed collagen, amino acid solutions, cellulose derivatives, or cellulose based polymer binders. Optionally, a coating, at about 1 wt % or less, may be added to the outer surface of the manufactured granular substrate.
The granular substrate of the present invention has a bulk density of less than about 55 pounds per cubic foot at a particle size guide number ranging from about 75 to about 300. The granular substrate should have a sufficiently high bulk density to provide the desired ballistics upon application of the finished product. In a first embodiment, the preferred bulk density is between 40 pounds per cubic foot and 55 pounds per cubic foot, and is most preferably greater than 42 pounds per cubic foot to about 52 pounds per cubic foot. Additionally, the substrates have a uniformity index at a minimum of 40. The particle size and bulk density are desirable properties for use of the granular substrate as a carrier for active chemical agents, such as herbicides or other pesticides. Additionally, the granular substrate resists attrition during handling but is preferably capable of breaking down once exposed to water.
In alternate embodiments, the granular substrate preferably has a bulk density of 40 pounds per cubic foot or less. Depending upon the desired application, the granular substrate may or not be readily water dispersible. In those applications where water dispersibility is desired, it is preferred that the granular substrates according to these embodiments of the invention have a water dispersibility of about 5 minutes or less.
The process of the invention involves the mixing and pelletizing of the noted manufactured granular substrate composition. The mixing of the present inventive composition occurs at relatively low shear forces to prevent the degradation of the mix components. The pelletizing of the mixture composition may be accomplished through conventional pelletizing equipment such as pelletizing pans or drum granulators. The manufactured granular substrate, in pellet form, is then generally dried at a temperature of about 240xc2x0 F. to about 300xc2x0 F. to remove excess moisture and produce the manufactured substrate of the present invention.
It is an object of the present invention to provide a manufactured granular substrate, produced from at least one mineral component and additional additives, that has a bulk density of about 55 pounds per cubic foot or less at a particle size in accordance with particle size guide number standards of about 75 to about 300. A manufactured granular substrate having the noted characteristics is desirable for use as a carrier for chemical agents because the granular substrate, in bulk form, has a greater surface area for receiving the chemical agent while reducing the amount of inert material required for application. Additionally, the smaller particle size and lower bulk density of the present invention result in an improved distribution of active chemical agents over a specified area.
It is also an object of the present invention to provide a manufactured granular substrate that does not degrade during handling, yet preferably disintegrates upon application and exposure to water.
In accordance with the present invention, it has been discovered that a combination of specific mineral components, light weight additives, and binders results in a preferred manufactured granular substrate which is suitable for use as a carrier for active chemical agents. Additionally, the present invention involves a process for manufacturing the granular substrate.
The present invention provides a granular carrier in pellet form that has a bulk density of less than about 55 pounds per cubic foot at a nominal product sizing, in accordance with the size guide numbering system, of about 75 to about 300. In certain preferred embodiments, the preferred bulk density is between about 40 pounds per cubic foot to about 55 pounds per cubic foot, and is most preferably greater than 42 pounds per cubic foot to about 52 pounds per cubic foot.
The manufactured substrate has an appropriate crush strength and resistance to attrition to prevent significant degradation of the substrate during handling. Additionally, the manufactured granular substrate quickly disperses when exposed to water. The granular substrate also has the appropriate spherocity, absorption, and solubility to enable the use of the substrate as a carrier for active chemical agents such as herbicides, plant growth regulators, insecticides, fungicides, or other pesticides.
The manufactured granular substrate of the present invention includes one or more mineral components preferably selected from the group consisting of dolomite, limestone, and gypsum. In these embodiments, the mineral components make up about 65 wt % or more of the manufactured granular substrate. In general, the mineral components have a sizing of 100% passing through a 30 mesh screen and 50% or more passing through a 200 mesh screen. The mineral components have a preferred sizing of about 100% through a 50 mesh screen and 80% or more through a 200 mesh screen. The noted mesh sizes and all those mentioned hereafter conform with U.S. standard sieve sizes. Additionally, the mineral components have a bulk density of greater than about 70 pounds per cubic foot, and preferably have a bulk density of about 75 to about 90 pounds per cubic foot. The sizing of the mineral components may vary with respect to other ingredients utilized in the agglomerated substrate. In addition to the preferred mineral components, other stone or mineral dust compounds conforming with the size and bulk density parameters may be suitable for use with the present invention.
One or more light weight additives are utilized with the present inventive composition to obtain the desired bulk density of the finished substrate. In these embodiments, the manufactured granular substrates include about 5 wt % to about 25 wt % of the additives. The light weight additives are generally inert compounds having a bulk density of less than 35 pounds per cubic foot and a sizing of at least 20% passing through a 40 mesh screen. It is preferred that the additives have a sizing of 100% passing through a 40 mesh screen. Additionally, the light weight material should be a non-fibrous material as indicated by the sizing parameters. Fibrous material can adversely impact the dispersibility and the flow characteristics of the finished granular substrate. The light weight additives are preferably selected from the group consisting of expanded silica, fly ash, hydrated lime, wheat flour, wood flour, ground wheat straw, cellulose and soy flour. However, other inert compounds meeting the bulk density and sizing specifications may be suitable for use in the present inventive composition.
A preferred embodiment includes the use of wood flour resulting from finely milled wood particle board. The wood particle board contains approximately 10 wt % of a urea-formaldehyde resin. Another preferred embodiment includes the use of wheat straw flour resulting from finely milled wheat straw particle board. The wheat straw particle board contains a diphenylmethane diisocyanate resin. In both cases, the additional resin assists in producing a granular substrate that does not degrade during handling but breaks down upon exposure to water.
A binder is utilized to agglomerate the ingredients of the present invention. In these embodiments, the binder is utilized at an amount up to about 20 wt % (dry basis) of the granular composition. The preferred amount of binder is generally 2 wt % to 20 wt %. The binder utilized will bind the ingredients into a granular substrate which resists attrition, will not degrade and therefore maintain their particle size during handling. The binder is such that the resulting granular substrate has a resistance to attrition (RTA) value, in accordance with ASTM E 728-91 Volume 11.04, of at least 85%. In addition, the selected binder needs to be sufficiently water soluble that the resulting granular substrate disperses quickly in water.
The binder is preferably selected from the group consisting of brewers condensed solubles, lignosulfonate, sodium carbonate lignin, cane molasses, beet syrup, beet molasses, desugared beet molasses, whey, starch, starch derivatives, soy solubles with cane molasses or the like, hydrolyzed collagen, amino acid solutions, cellulose derivatives, or cellulose based polymer binders. Other water soluble binders having equivalent properties to, for example, the brewers condensed solubles, may be suitable for use in the present inventive composition, although economics may mitigate against their use. If a more hygroscopic of the binders is selected, such as cane molasses, beet syrup, beet molasses, desugared beet molasses or whey, it may be desirable to also include one or more of the less hygroscopic binders, to improve the storability of the resulting granular substrates.
The binder is generally added to the composition as a solution. The solution is typically provided as a water based slurry having about 40% to 50% solids by weight and weighing about 10 pounds per gallon. The binder may also be added and mixed with the other dry ingredients, subsequently mixing in an amount of water.
Optionally, a coating may be included with the manufactured granular substrate to provide a harder outer shell. The coating is generally added to the composition at 1 wt % or less. The coating material is added directly to the dried, finished pellets and enhances the strength of the granular substrate to prevent degradation. The preferred coating material is polyvinyl alcohol. However, other coating compositions capable of strengthening the substrate without adversely affecting the desired properties are suitable for use with the present invention.
The composition of the present invention is generally produced by first creating an admixture of the noted components within the specified ranges. The mixing of the components may occur in either a batch or continuous mixing process. Conventional mixing devices are suitable for use with the present invention. The components should be thoroughly mixed at conditions which prevent degradation or compaction of the materials. During the mixing step, the binder composition is generally added to the mixture as a solution. Optionally, at least part of the water soluble binder may be added to the pelletizing apparatus during pelletizing. Additional water, up to about 15% by weight, may be necessary for agglomeration of the materials in the inventive composition.
The admixture is then fed into a pelletizing apparatus to produce the manufactured granular substrate of the present invention. Conventional pelletizing equipment is suitable for use in producing the substrate in pellet form. The preferred pelletizing equipment is a pelletizing pan. Additionally, drum granulators or other types of granulation equipment may be used to produce the granular substrate of the present invention.
Water may be added to the mixture during the pelletizing step of the process to assist in granulation of the material. The water is generally added at an amount which results in no greater than 35% by weight in the substrate.
In accordance with the present invention, the operation of a pelletizing pan may vary with the specific formulation or ingredients in order to produce a granular substrate with the preferred properties. For example, feed rates and locations of the admixture or the water, the angle of the pan, the speed of rotation of the disc, or the depth of the pan may be varied to produce the desired product. One skilled in the art of pelletizing is capable of recognizing the variables and making adjustments to obtain the granular substrate in pellet form.
The manufactured granular substrate is then dried to a temperature of about 240xc2x0 F. to about 300xc2x0 F. to remove excess water utilized during the agglomeration of the components.
The pellet is dried to a total moisture content of 8% or less in accordance with ASTM standard D 5033 Volume 11.04. The substrates have a preferred total moisture content of 2.0% or less. The upper temperature limitation during the drying step prevents the degradation or burning of the organic binder in the granular substrate. The substrates may be dried in conventional drying units such as for example a fluid bed dryer or a rotary dryer.
The resulting granular substrates are then screened to remove oversized and undersized granular substrates. The improperly sized material may be recycled to the mixing stage or milled to the appropriate size and rescreened. Optionally, the finished product may be sprayed with a light weight mineral oil to prevent dusting of the product in bulk form.
The sizing and bulk density are important finished product specification for the present invention. The composition of the present invention results in a relatively low bulk density while having a smaller particle size distribution. This is contrary to conventional, mineral based granular substrates, where typically larger particles have bulk densities in excess of 60 pounds per cubic foot. The resulting manufactured granular substrates of the present invention nave a bulk density, as measured by ASTM E 727 Volume 11.04 standards, of less than about 55 pounds per cubic foot, and preferably from about 40 pounds per cubic foot to about 55 pounds per cubic foot.
The size of particles is determined by the size guide number/uniformity index system used in the fertilizer industry. The substrates of the present invention have a size guide number between 75 and 300 and a uniformity index of at least 40. The size guide number describes the relative particle size and is obtained by multiplying the average particle size, in millimeters, by 100. The uniformity index is a comparison of large particles to small particles. The index is expressed as a whole number between 1 and 100 with higher numbers indicating better uniformity and tighter size range. Additionally, the sizing may be determined in accordance with ASTM E 728-91 Volume 11.04 wherein the sizing is preferably 20% or more passing through a 14 mesh screen and retained on a 40 mesh screen.
The manufactured granular substrate must be strong enough so that the particle does not degrade during normal conveying and handling operations. The degradation of granular substrates would result in an increase in fine material which in turn would increase the bulk density. Additionally, dust or powder material absorbs more chemical agent and therefore would result in the improper distribution of the active chemical agent upon application.
It is preferred that the granular substrate not degrade until subject to water. However, it is also preferred that the substrate not degrade with high humidity. The ability of the granular substrate of the present invention to degrade with water is generally measured in a water dispersibility test. The test involves placing about 10 grams of the granular substrate into 100 ml of water at room temperature in a closed glass container. The container is then inverted and the time is observed until the material completely disperses. After every minute, the container is inverted. The granular substrate of the present invention has a dispersibility time of generally less than 3 minutes.
The strength of the granular substrate is determined through the crush strength test, ASTM E 382 Volume 3.06, and resistance to attrition (RTA) test, ASTM E 728-91 Volume 11.04. The manufactured granular substrate of the present invention has a crush strength between 2 and 8 pounds on an 8 mesh pellet. Additionally, in these embodiments, the granular substrate has an RTA value of at least 85%.
The resulting granular substrate of the present invention generally has a smooth surface and is spherical in shape. The spherocity lends to desired flow characteristics of the substrates in bulk form. The angle of repose is a test utilized to measure the ability of a substrate to flow in bulk form. The test is conducted on a 14xc3x9730 mesh sample. The granular substrates of the present invention all have an angle of repose of about 35 degrees or less.
The granular substrate must have the capability of absorbing the active chemical agent in order to function as a carrier. The active agent is generally absorbed in the carrier up to about five percent by weight. The substrate is also water soluble and therefore degrades upon exposure to moisture or water.
The manufactured granular substrate of the present invention is suitable for use as a carrier for active chemical agents. For example, active chemical agents could include herbicides or other pesticides that are commonly distributed through the use of a carrier in bulk form.
The following examples, which constitute the best mode presently contemplated by the inventors for practicing the present invention, are presented solely for the purpose of further illustrating and disclosing the present invention, and are not to be construed as a limitation on the invention: